1. Field of the Disclosure
Embodiments disclosed herein relate generally to curable compositions and thermoset resins formed from such curable compositions. The curable compositions, for example, may include an admixture of cycloaliphatic epoxy resins or an admixture of a) a cycloaliphatic epoxy resin; b) one or more of a flexibilized cycloaliphatic resin, an epoxy phenolic novolac resin, an epoxy bisphenol A novolac resin, a multifunctional epoxy resin, a bisphenol-A or bisphenol F based epoxy resin, and a polyether polyol c) a catalyst; and d) one or more cycloaliphatic anhydride hardeners. Hardeners used in the curable compositions may include cycloaliphatic anhydrides.
2. Background
Epoxies resins are one of the most widely used engineering resins, and are well-known for their use in composites with high strength fibers. Epoxy resins form a glassy network, exhibit excellent resistance to corrosion and solvents, good adhesion, reasonably high glass transition temperatures, and adequate electrical properties. Unfortunately, crosslinked, glassy epoxy resins with relatively high glass transition temperatures (>100° C.) are brittle. The poor impact strength of high glass transition temperature epoxy resins limits the usage of epoxies as structural materials and in composites.
The impact strength, fracture toughness, ductility, as well as most other physical properties of crosslinked epoxy resins may be controlled by the chemical structure and ratio of the epoxy resin and hardener, by any added macroscopic fillers, toughening agents, and other additives, and by the curing conditions used. Typical performance requirements of thermoset resins, including epoxies, include a high softening point (>200° C.), low flammability, hydrolytic resistance, chemical and solvent resistance, and dielectric rigidity.
Performance criteria for the compositions during storage, cure, and for the thermoset resins formed from epoxies vary. In some industries, a slow curing resin may be acceptable, such as where the resin cures over an extended time period of hours or days. However, other uses require the curable epoxy compositions to have a high reactivity, curing only after a brief exposure to elevated temperatures. Unfortunately, high reactivity often leads to one or more undesired properties in the resulting thermoset resin.
Accordingly, there exists a need for epoxy compositions having a relatively low viscosity and a relatively high reactivity, and where the resulting thermoset resin has a good balance of a high glass transition temperature, tensile strength, tensile modulus, and elongation properties.